1. Field of the Invention
The present invention pertains to the field of optical systems and in particular to an optical system incorporating solid-state light emitting devices configured in an array.
2. Background Information
Recent innovations in LED design and manufacturing have led to the introduction of high-brightness LEDs that produce sufficient luminous flux for architectural and entertainment lighting applications. LEDs with different wavelength ranges, for example, red, green, and blue, have been combined in arrays with ancillary refractive optics to generate user-specified colours. An example of this type of configuration is the Space Cannon Metamorphosis™ (Space Cannon vH, Fubine, Italy), wherein an array of red, green, and blue LEDs with individual moulded plastic optics, produces a narrow beam of coloured or white light. An example of a device that can produce a broad “wash” of coloured or white light is the Color Kinetics ColorBlast™ 12 (Color Kinetics, Boston Mass.), which provides an array of red, green, and blue LEDs 20 mounted behind a frosted or clear tempered glass panel 40, as illustrated in FIG. 1.
The object of these light fixtures is to provide a narrow or broad distribution of light that has a uniform colour. However, the arrays of LEDs associated with these particular products consist of clusters of individual red, green, and blue LEDs that are provided in order to enable the satisfactory blending of the individually produced colours, thereby producing a user-specified colour on the illuminated surfaces. If, however, the LEDs are arranged in linear rows of separate colours, the projected beam of light typically exhibits objectionable colour gradients at its edges. In addition, surfaces being illuminated using the above mentioned devices, that have occluding objects thereon, results in strong colour banding being visible on the illuminated surface due to the shadow cast by this occluding object.
In addition, the above devices can include moulded plastic optics 30, as illustrated in FIG. 2, associated with each of the LEDs 20 to provide the control of the illumination. However these types of optics are bulky and relatively expensive to manufacture. Furthermore, these forms of refractive optics are unable to preferentially redirect emitted illumination in an off-axis direction, with respect to the plane of the array of LEDs, however this is possible if the LEDs are mounted at an angle with respect to the plane of the array. In order to enable this type of mounting, each LED could be mounted and wired separately to enable this form or orientation, however this would preclude the use of a common circuit board for the mounting of the LEDs, as is a current standard, thereby resulting in a more costly device.
A further disadvantage of the prior art is that red, green and blue LEDs typically require different drive voltages and can produce ranging colours of light, as such binning of LEDs is typically performed, in order to ensure a uniform illumination colour being produced by an array of LEDs. As such, LED manufacturers typically offer pre-assembled linear arrays of single colour LEDs with matched colours. For example, the Lumileds Line of products (Lumileds Lighting LLC, San Jose Calif.) comprise twelve high-brightness LEDs mounted in a row on a common printed circuit board. As has been previously mentioned, linear arrays of LEDs are difficult to incorporate into current lighting devices due to the problems of colour gradients and colour banding.
The prior art comprises a number documents that define the design and method of use of reflector arrays. For example, U.S. Pat. Nos. 6,260,981 and 6,439,736 both define a luminaire designed to be suitable for suspended ceilings, wherein the design of this luminaire enables an improved packing density of these products during shipping. The reflector is designed having a grid pattern with a tapered design that allows these reflectors to be stored and transported such that one reflector nested within another thereby conserving space.
U.S. Pat. No. 6,234,643 provides a lighting fixture for reducing glare and dark spots on ceilings and walls through the use of direct and indirect reflectors. This lighting fixture includes first and second sets of elongated, parallel, spaced apart reflectors that intersect at a ninety-degree angle thereby forming an open reflector grid. In addition, the lighting fixture includes a plurality of indirect reflectors connected to the outside walls of the open reflector grid which provide a means for reducing glare and dark spots on the ceiling and walls, which can be caused by the plurality of fluorescent lamps in the louver housing. This lighting fixture is designed specifically for use with fluorescent lamps and as such does not provide a means for manipulating the illumination provided by a plurality of discrete light sources that produce different wavelengths of illumination.
In addition, the design and method of making an array of optoelectronic devices is provided in U.S. Pat. No. 5,660,461. The array of LED is formed from a plurality of modular units, wherein a modular unit comprises a light emitting diode and a moulded reflector unit that has a cone shape. In order to assemble the array of optoelectronic devices, a plurality of the modular units are interconnected by a mechanical snap type connection. As such the modular units are fabricated individually and the use of a plurality of LEDs on a linear printed circuit board, as is common practice in the art, would not be applicable for this type of design.
The prior art further comprises a number of documents that disclose diffusers that are used for blending or distributing illumination in a plurality of directions. For example, U.S. Pat. No. 6,447,133 provides an illumination member having a diffuser that has therein a plurality of spheres or particles that have a different refractive index when compared to the diffuser material itself. As such, the illumination on the output face of the diffuser can be controlled by varying the number, size and homogeneity of these spheres or particles. Specifically, this diffuser has been designed such that is can be a few millimetres thick and have the ability to emit a homogeneously distributed luminance on its output face. This type of diffuser is specifically designed for use with a LCD display and provides a means for controlling the illumination there from. However this diffuser has not been designed to provide the blending of colours produced by a plurality of discrete light sources in close proximity.
U.S. Pat. No. 6,241,363 provides a coloured light mixing device that can be associated with at least one light source set, such that the light source set has three light generating units that generate light of different colours. The coloured light mixing device comprises a colour mixing plate that is made of transparent material and has a lower surface that has a lower wavelike pattern thereon that faces the light source set, and an opposite upper surface that has an upper wavelike pattern thereon. In addition, the upper wavelike pattern is oriented differently from the lower wavelike pattern. Upon being hit by light from the light source set, the lower wavelike pattern acts as a plurality of linear light sources for mixing light colours inside the colour mixing plate and the upper wavelike pattern thereby emits light of uniform intensity and mixed hue. This design of a diffuser enables colour mixing specifically designed for the situation where there is close proximity between the various colours of light and therefore may not be effective in blending illumination produced by a first strip of light emitting devices producing a first colour that is flanked by a second strip producing a different illumination colour.
Finally, U.S. Pat. No. 6,264,346 provides an apparatus for mixing light from different coloured LEDs. This apparatus comprises a faceted diffusive layer that is used to mix light from an LED array and is more specifically designed for the creation of white light from these different coloured LEDs. This type of apparatus essentially directs all of the illumination from the multiple different coloured light emitting diodes in the same direction thereby combining them to form the desired illumination colour, namely white light.
Therefore there is a need for a new method and apparatus for the manipulation of illumination created by an array of light emitting devices that is capable of reducing colour gradients and colour banding in addition to being optically efficient and capable of illumination distribution in an off-axis direction of the light emitting device array, while being applicable for use with strips of single coloured light emitting devices, as are commonly produced in the industry.
This background information is provided for the purpose of making known information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.